This invention relates generally to freight train brake control systems, and more particularly, to an apparatus and method for a pneumatically controlled graduated release of brake cylinder pressure in a freight train brake control system.
In conventional freight train braking systems controlled by a pneumatic control valve, pressurized fluid is utilized to control braking functions on each car of the train. One or more locomotives and each car are interconnected by a brake pipe which supplies pressurized fluid from a main reservoir on the locomotive to reservoirs on each car. Each car in a standard pneumatically operated freight braking system has onboard a reservoir, typically divided into emergency and auxiliary compartments which are charged via the brake pipe, a pneumatic control valve (PCV) and a fluid pressure activated brake cylinder device. The PCV selectively communicates between the brake pipe, each reservoir compartment, the brake cylinder device and the atmosphere. The PCV controls the operation of the brakes on the car by controlling the access of pressurized fluid between the brake cylinder and the reservoirs or the atmosphere. The operation of the PCV is controlled by the engineer from the locomotive by adjusting the pressure in the brake pipe. Basically, a reduction in brake pipe pressure signals the PCV to admit pressurized fluid from a reservoir into the brake cylinder device to apply the brakes. Conversely, an increase in brake pipe pressure signals the PCV to vent the brake cylinder to the atmosphere thereby releasing the brakes.
Overall, the conventional pneumatic braking system utilizing the PCV has proven to be a very safe and reliable system. However, a couple of disadvantages of the PCV controlled system are that it takes time for the pressure change initiated at the locomotive to propagate throughout what may be hundreds of cars. As a result, the PCV on each car senses the pressure change sequentially such that the brakes on each car are applied in sequence rather than simultaneously. The PCV on cars near the locomotive will sense the pressure change sooner and thus the brakes on that car will be applied in advance of the brakes on cars down the line.
Another disadvantage is that once the brakes are applied, the only way to release them is to vent the brake cylinder to atmosphere, thus completely exhausting all pressure from the brake cylinder. In other words, the brake cylinder pressure cannot be partially reduced. Either all of the pressure must be kept or it all must be dumped. Furthermore, once the brake cylinder pressure is vented it can take time to recharge the brake pipe and reservoirs sufficiently to make further brake applications.
Prior art devices include the use of retainer valves with ABDW, ABDX type equipment to xe2x80x9cretainxe2x80x9d a portion of the brake cylinder pressure upon a direct release.
A relatively recent development in freight train braking controls is the Electrically Controlled Pneumatic (ECP) brake control system. In a conventional ECP system, an electronic controller (EC) is provided on each car along with solenoid operated valves which control the exchange of pressure between the brake cylinder device and the reservoirs or the atmosphere, basically taking over the functions of the PCV. Thus, the EC directly controls the brake cylinder and may be referred to as a brake cylinder control (BCC) type ECP system.
Initially, this BCC type ECP system has been tested as an overlay system on the conventional pneumatic system, with the PCV functioning as a back-up brake control device. However, all electronic BCC type ECP brake control systems are being prepared and the American Association of Railroads (AAR) is in the process of promulgating certain requirements regarding minimum equipment and operating conditions for such ECP systems.
One of the advantages of the BCC type system is that the EC is electrically signaled from the locomotive to operate the brake cylinder device. Thus, the brake signal is propagated essentially instantaneously and the brakes on every car can be actuated at virtually the same time. Another advantage is that the level of brake cylinder pressure is adjustable because the solenoid valves can partially vent brake cylinder pressure without completely exhausting all of the pressure to the atmosphere. As a result, the engineer can signal the EC to increase or decrease the braking force by any amount desired.
However, one disadvantage is the cost of implementing such an ECP system. For example, the AAR minimum requirements include, among other things, the requirement of a 2500 W power source on the locomotive, a 230 VDC trainline cable and a communications device one every car each with having a battery as a back-up power source. These requirements impose a significant cost factor.
Accordingly, there is a need for a device which provides a pneumatically controllable graduated release of brake cylinder pressure to obtain the graduated release advantages of the ECP system without the need for all of the associated electrical equipment and costs.
A release graduating valve (RGV) according to the invention is preferably integrated into a pneumatic control valve, such as an otherwise standard ABDX, or ABDX-L, for use in either conventional pneumatically braked freight trains, or in unit trains of similarly equipped cars.
In normal freight train service, the RGV must provide direct release in concert with all other cars in the train, many or most of which typically would not be equipped with an RGV. Consequently, the RGV preferably includes a changeover valve portion for selectively switching between a graduated release mode and a direct release mode.
In the conventional direct release mode, the changeover valve isolates the graduated release portion of the RGV to permit the PCV to exhaust brake cylinder pressure in a conventional manner. In the graduated release mode, the changeover valve interposes a metering valve portion which exhausts brake cylinder pressure generally proportional to a reduction in pressure in the brake pipe.
The changeover valve can be selectively actuated responsive to the pressure in a secondary trainlined air pipe, for example a main reservoir pipe, which is supplied with pressurized fluid from a remote source. Alternatively, the changeover valve can be responsive to brake pipe pressure such that a secondary trainlined air pipe is not necessary. In this case, a brake pipe sensor valve portion can additionally be provided for controlling the activation of the RGV.
As an alternative to the selectively operable configuration, the RGV could also be provided in a xe2x80x9cpermanentxe2x80x9d version. A permanent RGV is one in which there is no changeover valve portion to permit an optional direct release. Thus, brake cylinder pressure can routinely be exhausted in a graduated manner.
In any event, the selectively actuable RGV is the presently preferred type. Any car equipped with a selectively operable RGV would be capable of operation in a train of standard (non-equipped) cars for switching, positioning of equipment, and simply allows the fullest, most economical use of the car in any service for which it was otherwise suitable, without special handling procedures.
In a unit train of similarly equipped cars, graduated release operation of the individual car brakes can provide several benefits, and this may be one application for the xe2x80x9cpermanentxe2x80x9d version. For example, the partial release of brakes may permit reduction of friction braking as a train slows to the desired speed on a downgrade, in order to use a higher percentage of dynamic braking to retard the train, with the benefit of reducing wear of the friction brake shoes. Additionally, the gradual release of brakes provides smoother control of slack, reducing inter-train forces and the damage it can cause. This is especially true when pulling a train out of a xe2x80x9csag.xe2x80x9d Moreover, a saving of air and locomotive fuel will be realized. This savings resulting from being able to reduce braking in undulating territory and avoid either slowing the train unnecessarily or applying wasteful power braking in order to avoid releasing the brakes. This situation occurs when the train is slowing below the desired speed, but the engineer realizes that heavier braking will be required on a downgrade ahead. The availability of graduated release avoids the necessity to completely release brakes, thereby saving the air and time that would be necessary to re-apply them to a higher degree when needed on the increased downgrade. A unit train of cars equipped with the release graduating valves described herein can use the graduated release feature to provide improved brake performance.
Further details, objects, and advantages of the invention will become apparent from the following detailed description and the accompanying drawings figures of certain embodiments thereof.